Electrical power is typically acquired from chemical energy carriers by combustion and by utilization or further conversion of the resulting hot gases in generators. A more direct conversion possibility is offered by fuel cells. In a combination of fuel cell and electric motor, for example, in the case of vehicles, a higher efficiency is achieved than in vehicles having conventional internal combustion engines. Hydrogen-oxygen fuel cells are primarily used. A fuel cell consists of electrodes, which are separated from one another by a semipermeable membrane or an electrolyte.
The electrode plates or bipolar plates usually consist of metal, graphite, or other conductive materials. The energy is delivered by a reaction of oxygen with the fuel, generally hydrogen. Both reaction partners are continuously supplied via the electrodes.
An exemplary construction is illustrated in FIG. 2. As an example, a fuel cell of a low-temperature proton exchange membrane fuel cell (PEMFC) is illustrated here. The structure of the fuel cell 20 is formed by two bipolar plates, which are identified with the reference sign 53. The cathode side is marked with the reference sign 57 in this case, and the anode side with the reference sign 58. The bipolar plates have milled-in gas channel structures. They consist, for example, of coated metals or conductive plastic, which becomes electrically conductive due to the addition of carbon nanotubes. The two bipolar plates 53 are mounted and connected to one another, as illustrated on the left and the right in the drawing, by sealing end fittings 54. A membrane electrode unit 56 is arranged in the middle between the two bipolar plates and mounted by the sealing end fittings 54. The catalytically coated surfaces of the membrane electrode units are the chemically active layers, on which the reaction occurs. The membrane 56 is proton-conductive, but is gas-tight and does not conduct electrons.
The membrane 56 is located in separate gas chambers 52 and 52′. Hydrogen is introduced as a combustion material into the gas distribution chamber 52′ via the anode side 58 through the milled channels 55. Oxygen or air is distributed on the cathode side into the gas distribution chamber 52 via the gas channels 51. Protons from the gas distribution chamber 52′ travel through the membrane 56 and react with the oxygen ions on the active layer of the membrane to form water.
The electrolyte which is used is resistant to CO2, however, it has a certain sensitivity in relation to carbon monoxide. Since the reactions run at relatively low temperatures, the tolerance in relation to carbon monoxide represents a problem, since excessively many catalytically active centres of the membrane surface may be blocked by CO molecules.
PEM (proton exchange membrane) fuel cells require an air compressor. In systems having PEM fuel cells, at least one electrical compressor or a turbocharger is therefore used on the air supply side, wherein the attachment is performed via bearings.
The bearing point, which is typically located between the air compressor and a drive motor, cannot be lubricated using lubricants on an oily basis, since even ultrasmall quantities of oil reaching the fuel cell as a result of leaks would damage the fuel cell irreversibly. Therefore, costly bearing concepts such as ceramic bearings are required for such applications in conventional devices.
Turbochargers having lubricants on an oily basis also cannot be used in a PEMFC system, since oil particles already reach the cathode side of the fuel cell and irreversibly damage it in the event of ultrasmall leaks of the sealing rings.
To avoid this, turbochargers are used, which usually have a lubricant-free ceramic bearing concept, which rotates magnetically positioned on an air cushion or using other material concepts. These compressors rotate in a very high speed range and are very costly to implement.
Fuel cells are known from the prior art, in which a water circuit is used. A system is described in German Patent Publication No. DE 19945323 A1, in which water is used for the purpose of humidifying the process air, to obtain good conductivity for protons through the membrane, and furthermore is used for cooling and lubricating the gas compressor.
A system made of compressor and decompressor is known from Chinese Patent Publication CN 1423356A, which is operated for a fuel cell having an oil-free lubricant.
The solutions selected in the prior art have the disadvantage that the lubricating circuits and the humidification circuits of the fuel cell are not separate. Connecting the fuel cell to the components of a vehicle or a stationary plant system and integration of the lubricating circuits is therefore not possible in a simple manner.